Sources familiar with the matter tell ABC News first lady Melania Trump sponsored both her parents' green card application, a move which eventually led to their gaining U.S. citizenship on Thursday through a process that the president has derisively called “chain migration”.

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The first lady's parents, Viktor and Amalija Knavs, were sworn in as U.S. citizens at a federal immigration court in New York City.

"Citizenship was just awarded," the Slovenian couple's immigration lawyer Michael Wildes said after accompanying them to the courthouse.

When ABC News asked whether Melania Trump sponsored her parents, Wildes deflected the question and responded that "they applied on their own."

Wildes did not elaborate on exactly through what means or program the couple became citizens.

"Everything was through a normal process. Like everybody else here you're allowed to apply after five years of having your green card and so forth. It was all done lawfully," Wildes told reporters.

Wildes' response does not clarify whether the Knavses obtained citizenship through what their son-in-law President Donald Trump has derisively called "chain migration" or whether the first lady did indeed sponsor them.

"They have travailed a wonderful journey like most have – millions have – in getting citizenship and waiting the requisite period of time," Wildes said. "The application, the process, the interview was no different than anybody else's other than security arrangements to facilitate today."

In February, the Knavses were confirmed as permanent residents of the United States after emigrating from Slovenia by Wildes.

Seth Wenig/AP

Parents of First lady Melania Trump, Viktor and Amalija Knavs, listen as their attorney Michael Wildes, makes a statement in New York City, Aug. 9, 2018.

"I can confirm that Mrs. Trump’s parents are both lawfully admitted to the United States as permanent residents," Wildes said in a statement to ABC News in February. "The family, as they are not part of the administration, has asked that their privacy be respected so I will not comment further on this matter."

At the time, Wildes would not say how the Knavses received green cards to live and work in the U.S.

Immigration experts told ABC News in February that the most likely way the Knavses could have become permanent residents is through their daughter’s citizenship.

"The most obvious way that they would have become green card holders is by being the parents of a U.S. citizen – i.e. Melania Trump," said Stephen Yale-Loehr, an immigration professor at Cornell Law School.

This is a process that Trump has consistently referred to as "chain migration." The legal status of the president's in-laws has come under scrutiny after the Trump administration’s proposed crackdown on the process.

AP

In this Saturday, Aug. 4, 2018 file photo, President Donald Trump speaks at a rally at Olentangy Orange High School in Lewis Center, Ohio.

Trump’s hard-line stance on immigration has shaped his administration’s agenda, after he persistently attacked the process and the broader system. As part of his administration’s proposed overhaul of the current immigration system, Trump made clear that ending chain migration is one of his key priorities — touting it as the fourth pillar of his reform plan in his first State of the Union address.

"Under the current broken system, a single immigrant can bring in virtually unlimited numbers of distant relatives," he said in January.

The term "chain migration" describes the process by which American citizens sponsor their relatives for immigration to the U.S.

As one of the harshest critics of the process, Trump even alleged during the State of the Union that along with the visa lottery program, chain migration was a catalyst for two terrorist attacks in New York.

"In recent weeks, two terrorist attacks in New York were made possible by the visa lottery and chain migration," he asserted.

But in fact, despite both men who carried out the attacks entering the country legally through the two programs, they were not radicalized until after they arrived in the U.S., categorizing these incidents as homegrown.

The Knavses came to the U.S. from Sevnica, an industrial town in Slovenia.

Now Americans, the Knavses smiled for cameras, but remained silent.

“This golden experiment, these doors that are in America remain hinged open to beautiful people as they have today,” Wildes said.

He added they would appreciate their privacy and thanked everyone for “their attention to this very important dialogue that we're having on immigration. This is an example of it going right."

Wildes said the Knavses are “very excited.”

The first lady's office did not immediately respond to ABC News' request for comment.